Lithography methods have been frequently used for the production of fine structures in various kinds of electronic devices, such as semiconductor devices and liquid crystal devices. However, as the device structures are miniaturized, resist patterns in lithography processes are also desired to be miniaturized.
In the advanced field, for example, a lithography process now allows the formation of a fine resist pattern having a line width of about 90 nm. However, finer pattern formation will be required in future.
For attaining the formation of such a fine pattern having a line width of less than 90 nm, a first point is to develop an aligner and a resist corresponding thereto. Common factors to consider for developing the aligner include shortening of wavelengths of optical sources such as F2 excimer laser, EUV (extreme UV light), electron beam, X-ray, and soft X-ray, and increases in numerical aperture (NA) of lens.
However, the shortening of optical wavelength may require a new expensive aligner. In addition, even the resolution increases, a disadvantage of lowering a focal depth width occurs at high NA due to a trade-off relationship between the resolution and the focal depth width.
Recently, as a lithography technology for allowing such problems to be solved, a method known as a liquid immersion lithography process has been reported (e.g., Non-Patent Documents 1, 2, and 3). In this process, liquid refractive index media such as pure water or a fluorine-based inert liquid (refractive index liquid, and immersion liquid) lies in predetermined thickness on at least a resist film between a lens and the resist film. In this method, the space of an exposure light path conventionally filled with inert gas such as air or nitrogen is replaced with a liquid having a larger refractive index (n), for example pure water to attain high resolution without a decrease in focal depth width in a manner similar to the use of a light source of shorter wavelength or a high NA lens even if the optical source having the same exposure wavelength is employed.
Such liquid immersion lithography has been remarkably noticed because the use thereof allows a lens implemented in the existing device to realize the formation of a resist pattern excellent in higher resolution property as well as excellent in focal depth in low costs.
(Non Patent Document 1) Journal of Vacuum Science & Technology B (J. Vac. Sci. Technol. B) (Issued country: U.S.A.), vol. 17, No. 6, pages 3306-3309, 1999.
(Non Patent Document 2) Journal of Vacuum Science & Technology B (J. Vac. Sci. Technol. B) (Issued country: U.S.A.), vol. 19, No. 6, pages 2353-2356, 2001.
(Non Patent Document 3) Proceedings of SPIE (Issued country: U.S.A.), Vol. 4691, pages 459-465, 2002.